Immuno-serological diagnosis is carried out by sensitizing a carrier latex with a serologically active material such as an antigen or antibody, combining the serum to be tested with the latex, and allowing agglutination to take place in the latex, resulting in the detection of the presence of the corresponding antibody or antigen in the serum. Because of its ease and quickness, the immuno-serological diagnosis is widely applied to reagents in the clinical examination art in order to detect a variety of antigens or antibodies.
For this type of diagnostic reagent, carriers to be sensitized with an antigen or antibody are generally formed of resin latices, for example, latices of polystyrene and styrene-butadiene copolymers. These resin latices are required to form a stable emulsion, not to agglutinate during sensitization with an antigen or antibody, and not to agglutinate upon contact with a negative serum when the latices are observed for agglutination by reacting with an antibody or antigen which corresponds to the sensitizing antigen or antibody, that is, to be free of nonspecific agglutination.
Presently, not only qualitative, but also quantitative determination of trace amounts of a material such as antigen or antibody are crucial in the field of immuno-serological diagnostic examination. A prior art practice is the qualitative detection of a subject material being tested which is carried out by mixing and reacting a sensitized latex with the subject material to be tested on a glass plate and visually observing the agglutination of the particles in the latex. Numerous attempts have been made to achieve quantitative detection by a measurement using an optical instrument such as a spectrophotometer, turbidimeter, and quasi-elastic scattered light meter instead of the visual observation of agglutination. A method of detecting a reduction in tubidity of supernatant by utilizing the phenomenon that particles agglutinate in the sensitized latex, and a method of measuring a variation of absorbance or scattered light due to agglutination of particles in the sensitized latex, are known. See CROATICA CHEMICAACTA, 42. 457 (1970), Immunochemistry, 12, 349 (1975), and Japanese Patent Application Kokai Nos. 53-24015 and 54-109494.
These methods achieve quantitative measurement by determining the variation of the optical properties, such as absorbance and scattered light intensity, of a reaction system due to the immuno-serological agglutination of particles in a sensitized latex. However, these methods are not sufficiently accurate and are not capable of consistent reproduction because only a small variation occurs in the optical properties of a reaction system due to the agglutination. Further, quite often the optical properties of a sensitized latex will change with time, which creates a problem for obtaining a practical measurement.
A latex may be sensitized with an antigen or antibody either by physical adsorption or by chemical bonding. Because an adsorption-dissociation equilibrium does exist between the latex and the antigen or antibody with which the latex is sensitized, a commonly used sensitization method based on physical adsorption would have the drawback that there is the possibility of the antigen or antibody dissociating from the latex during measurement or storage.
It is, therefore, an object of the present invention to provide a carrier latex for use as a diagnostic reagent which is free from the above-mentioned problems of conventional diagnostic reagent carrier latices, and can be used in an immuno-serological diagnostic test utilizing an antigen-antibody reaction while experiencing minimized nonspecific agglutination reaction. Another object is to provide a carrier latex which is suitable for the optical measurement of absorbance and scattered light intensity.